This invention relates to a control valve suitable for controlling the pressure of exhaust gases entering the turbocharger of an internal combustion engine so as to control the air pressure to the engine.
Many internal combustion engines are turbocharged, predominantly diesel engines, but also including some gasoline engines in recent years. A turbocharger is, in essence, a combined air compressor and gas turbine. The engine's exhaust gases flow though the turbine, rotating it and also the compressor. The compressor supplies high pressure air for the engine so that the air and fuel mixture is at a density above atmospheric pressure. Engine power is directly proportional to the cylinder charge density. A typical turbocharger installation includes a control mechanism for regulating the pressure of air entering the inlet manifold of the engine. One form of control is to throttle, or vent to atmosphere, some of the air from the turbocharger. This type of control is inefficient because the input energy for the turbine is not reduced in proportion to the output of the compressor.
Another form of control is to vent to atmosphere some of the exhaust gases which would otherwise would drive the turbine. This can be accomplished by a simple springloaded release valve. Preferably, however, the venting of the exhaust gases is regulated according to the compressor air pressure. The air pressure is directed to act against a piston or, alternatively, a diaphragm. A diaphragm is preferred because it is cheaper and frequently more reliable than a piston.
Depending upon the fuel system of the engine, some compressors discharge an air-fuel mixture instead of fresh air. In this case, it is important that the valve motor be leakproof to avoid the fire hazard of an escaping air-fuel mixture, gumming of the valve stem and dilution of the air-fuel mixture for the engine.
As for any control system, it is desirable to achieve stability, that is, to use a valve action which seeks equilibrium, rather than one which prevents it. For a lift valve, also called a poppet valve, the alternatives are to open the valve into an exhaust stream or move the valve away from it. If the valve opens into the exhaust stream, the pressure of the exhaust gases interfers with the opening of the valve, and the opening of the valve causes a sudden pressure loss which causes the valve to close. Consequently, the valve must move away from the exhaust stream for stable action. Normally, this requires the valve motor to pull the valve towards it, and thus a piston or a diaphragm may utilize a connecting rod passing through a gland. To design a gland and piston which are leakproof is not impossible, but a reliable and heat resistant valve of this type is usually expensive.
It is therefore desirable to provide a valve which uses a non-perforated diaphragm and a glandless action, yet has the following desirable characteristics:
(1) Leakproof construction; PA1 (2) Stable action; PA1 (3) Accuracy over a fairly wide flow range; PA1 (4) Reliability; PA1 (5) Durability; PA1 (6) Compact size and convenient shape for mounting; PA1 (7) Adjustability; and PA1 (8) Inexpensive construction.
In earlier U.S. patents, valves employing nonperforated diaphragms and pressure plates on the opposite side of the diaphragm from the pressure inlet include U.S. Pat. Nos. 1,921,551 to Temple and 1,879,413 to Muller. These valves are, however, relatively complex and are not adapted for such uses as turbocharger control. Other control valves are found in U.S. Pat. Nos. 3,421,314 to Michalke, 4,130,266 to Bertling and 4,135,697 to Brumm.